Physical vapor deposition (PVD) is one of the most commonly used processes in the fabrication of semiconductor industry. The PVD process is a plasma process performed in a vacuum chamber where a negatively biased sputtering target is exposed to plasma of an inert gas having relatively heavy atoms such as argon (Ar) gas or a gas mixture comprising such inert gas. Bombardment of the sputtering target by ions of the inert gas results in ejection of atoms of the sputtering target material. The ejected atoms accumulate as a deposited film on a substrate placed on a substrate support disposed within the chamber.
In the PVD process, film compositions of the deposited film and controlling of the film composition variation during sequential wafers processing are restricted by the composition of the sputtering target. As known in semiconductor industry, various compositions of layers of metal gates are required to meet various electrical-property requirements such as drain current (Id) and tunneling voltage (Vt) of a transistor, and most layers of metal gates are fabricated by the PVD process.
Drain current (Id) and tunneling voltage (Vt) are key factors of the transistor and are highly correlated to the film composition of metal gates. Controlling of the film compositions of the deposited film and the film composition variation during sequential wafers processing has become serious and important issue in the PVD process. Accordingly, improvements in controlling of the film compositions of the deposited film and the film composition variation during sequential wafers processing for physical vapor deposition continue to be sought.